Say e.g. you create a tracker by copying an existing workflow for which some field permissions have been specifically set.

Deselecting the fields used by the tracker (at creation time or at a later time) doesn't remove these permissions.

The may lead to some ??Version Id can't be blank?? error message at issue form status update if the original workflow stated that the field is mandatory for the new status even if the ??Version Id?? field is not in the form.

This is not easy to determinate as the workflow permissions are not visible in the administration screen but only in database.